1. Field of the Invention
The present invention relates to a system and method for aligning the beam path of a beam-emitting sensor arranged on a motor vehicle.
2. Description of the Related Art
In distance regulating systems for motor vehicles, the motor vehicle has a radar or laser sensor which is used to detect one or more objects situated in the vehicle""s direction of travel. In order to accomplish this result, the sensor outputs a signal which is reflected by the objects. The reflected beam is received by the sensor again and evaluated in an evaluation circuit. The evaluation circuit performs an analysis of the signals and determines the relative vehicle speed, the distance of the vehicle from the detected object, and the lateral course deviation of the vehicle traveling in front from the vehicle""s direction of travel.
If the beam direction of the sensor is imprecise, objects are detected which are not of interest or important to consider. If the wrong vehicle is recognized as being the nearest to the vehicle, the distance regulator is set to this object, which can result in dangerous situations in road traffic and can possibly lead to a collision.
Particularly when determining the lateral deviation of the target from the vehicle""s direction of travel, inaccuracies in the angular error may result in significant errors for the calculated lateral course deviation as the distance from the located target increases. Since the sensors used have detection ranges of up to 150 m, then, at this distance, an alignment error angle at the vehicle of one degree would result in an error of approximately 2.9 m. Because the width of the roadway is approximately 3.5 m on average, this means that it is very quickly possible for the target to be incorrectly assigned to the predetermined lane for the vehicle which is to be controlled.
The present invention is therefore based on the object of specifying a method and a device which can be used to set the beam direction of the beam-emitting element on the motor vehicle conveniently and yet very accurately.
The invention achieves the object in that, when the vehicle is stationary, an external aligning beam hits a strictly planar surface on the sensor which reflects the aligning beam, the incident aligning beam and the reflected aligning beam are made to overlap as a result of the position of the sensor being changed.
The advantage of the method is that the setting accuracy depends only on the accuracy of the positional determination in front of the vehicle, the light source and the projection plane with respect to one another and the position of the reflective surface with respect to the sensor detection range. The absolute position of the reference surface with respect to the projection plane and to the light source is negligible in this case. In addition, there is no need whatsoever to take into consideration the installation tolerances of the system on the vehicle. For example, the absolute position of the sensor with respect to the center of the vehicle or above the ground below or the road is irrelevant. Hence, the influence of undercarriage variants, for example lower sports undercarriages, or manufacturing tolerances in the region of a few centimeters between two vehicles is also eliminated.
The method according to the invention enables the sensor to be aligned reliably both in the horizontal (azimuth) and in the vertical (elevation).
To align the azimuth, the aligning beam propagates along or parallel to an actual direction of travel of the motor vehicle. Since the sensors used can only produce a detection range of a few angular degrees in the horizontal, it is particularly important to be able to set small angular changes reliably as well using the method according to the invention.
The action for aligning the vertical is similar. In this case, the aligning beam is oriented to a planar vehicle tire contact area. The vehicles are aligned when carrying no load at the end of the production line in the factory. Since vehicles are usually loaded when the distance regulator is operating, the position of the detection range with respect to the ideal line (the horizontal) is rotated in elevation. On top of this, vehicles pitch to a very considerable extent when driven, that is to say the vehicle executes a vertical movement about the vehicle""s center of gravity. This happens, amongst other times, when starting off and accelerating or when braking. Furthermore, the detection range is also severely limited when the vehicle is climbing and descending.
In one refinement of the invention, before it hits the sensor, the aligning beam appears perpendicularly from a projection plane which the reflected beam hits and forms an image thereon. With the aid of such a projection plane, it is easy to ascertain a deviation between the emitted aligning beam and the reflected aligning beam.
The diameter of the aligning beam is advantageously approximately constant at least in the region between the projection plane and the sensor. In this case, the diameter of the light beam must be selected to be such that the smallest adjustment displacement is many times greater than the diameter of the light beam. This prevents errors in the alignment as a result of expansion of the light beam.
In one embodiment, the aligning beam is a laser beam which has a high constancy over a long path. The light beam can also be an infrared light beam. The vehicle""s direction of travel advantageously corresponds to the actual driving axis of the motor vehicle. This actual driving axis is determined using vehicle axle measurement methods which are known per se. Hence, devices such as axle test benches already used today can be used to determine the vehicle driving axis. Additional aids for determining the actual direction of travel of a vehicle are not necessary.
The optical axis of the aligning beam is oriented to the vehicle""s direction of travel either by orienting the vehicle or by orienting the aligning beam. In an apparatus for aligning a beam-emitting sensor arranged on the motor vehicle, a radiation source which emits an aligning beam is arranged behind a projection plane which lets through the aligning beam, and the aligning beam which passes through the projection plane hits a reflective surface mounted on the sensor in a repentable position with respect to the sensor. The reflected beam can be imaged on the projection plane via adjustment of a device which locks the sensor on the vehicle and coordinates the image of the reflected aligning beam with the emitted aligning beam in the projection plane.
In this case, the sensor can be arranged on the front, on the rear or else on the sides of the motor vehicle. In one embodiment, the projection plane has an opening through which the aligning beam passes, the center point of the opening coinciding with the optical axis of the light source. This ensures that it is not necessary to switch on the radar sensor or laser sensor for alignment. The precise setting of the beam direction of the sensor is ensured only using external aids.
In one simple embodiment, the projection plane is designed as a matt plate which can image the reflected beam. Hence, information is simply obtained about the direction in which the adjusting device must be moved in order to make the emitted aligning beam and the reflected aligning beam overlap.
A convenient embodiment of the invention is achieved in that the projection plane is designed as an active CCD linear array which is connected to the adjusting device via a control device. This makes electronic evaluation of the distance of the aligning beam from the reflected beam possible. Here too, the control device drives the adjusting device separately in terms of azimuth and elevation, until coordination is obtained.
In one refinement, the reflective surface is formed by an auxiliary device which is locked on the sensor by means of a three-point support. This three-point support gives the auxiliary device a defined position with respect to the reference surfaces and thus with respect to the detection range of the sensor. Each point of the support then correlates to a reference surface on the sensor.
In another refinement, the reflective surface is a reflective surface milled on the sensor housing itself. Auxiliary devices for providing the reflective surface can then be dispensed with. In one simple embodiment, the reflective surface is formed by a reflective plastic surface.